Update example/constants/example_constants.f90

Co-authored-by: Jeremie Vandenplas <[email protected]>

Author: MilanSkocic

example/constants/example_constants.f90

@@ -8,7 +8,7 @@ program example_constants
     print *, "speed of light in vacuum= ", c
 
     ! Use of mathematical constants such as PI
-    print *, "PI as double precision real= ", PI
+    print *, "PI as double precision real= ", pi
 
     ! Use codata_constant type for evaluating the value to the desired precision
     print *, "Value of alpha... evaluated to double precision=", alpha%to_real(1.0_dp)